1. Field of the Invention
This invention relates to a group of aminofunctional silane coupling agents which find uses as finishes for glass fabrics in the preparation for epoxy lamination composites, e.g. for printed circuit boards (PCB), with better performance than the previously known compounds. In particular, the present invention relates to the synthesis and use of certain arylalkyl aminofunctional silanes, which can be prepared using lower cost, more readily available non-styryl raw materials than that currently used.
2. Description of the Related Art
In fiberglass-reinforced plastics manufacturing, organofunctional alkoxysilanes (commonly referred to as ‘coupling agents’) are applied to glass fabrics to improve the glass/matrix interface bonding strength and at the same time to prevent penetration of moisture into the interface. Of particular interest to PCB industry which employs epoxy laminates, aminosilanes derived from chloromethylated arylenes, such as Z-6032 and Z-6224 of Dow Coming, A-1128 of OSi (now part of Crompton), are most commonly used. It is well known in the art that in the making of fiberglass reinforced epoxy laminates a process comprising: (1) treatment of glass fabrics with silane solution, (2) impregnation with epoxy resin, and (3) curing at an elevated temperature is involved. In the first step, silane solution in aqueous system is prepared and deemed most desirable for glass-fiber-finishing operations both from the standpoint of cost and safety because of non-flammability. U.S. Pat. No. 3,819,675 discloses a wide variety of cationic unsaturated aminofunctional silane coupling agents for composite applications. One particular composition that has attained remarkable commercial success is styryl aminofunctional silane having the formula:CH2═CHC6H4CH2NH(CH2)2NH(CH2)3Si(OCH3)3•HCl(Z-6032)in applications covering a wide range of polymeric composites. As such, it has gained a status of ‘universal’ coupling agent, i.e. one that can be used equally well for bonding organic polymers (including polyolefins, unsaturated polyesters, phenolics, epoxy resins, etc.) to inorganic materials. Most unsettling, however, is the question whether the styryl double bond in silane is needed for non-vinylic polymers such as epoxy resins but nevertheless, Z-6032 and its low HCl form Z-6224 have commended a predominant position in epoxy laminates applications for the last three decades, despite the high price. The high price is due to its raw material chloromethyl styrene, CH2═CHC6H4CH2Cl, which is available only from very few sources due to high costs associated with difficulty in manufacturing and product instability, which requires cooling during transportation and storage to prevent polymerization. A-1128 having the formula C6H5CH2NH(CH2)2NH(CH2)3Si(OCH3)3•HCl derived from a simple chloromethylated arene, benzyl chloride, is a lower cost product but represents a much smaller market presence because of the disadvantage in exhibiting weaker water resistance. Finding a viable alternative product thus becomes imperative.